No one is put to death for personal use. Only if you possess large enough quantities that makes you a dealer peddling typically peddling cannabis to large groups of people including underage kids.
I personally don't believe in death penalty and I hope it's abolished entirely. But facts needs to be stated with clarity.
Also Lee Kwan Yew is a legend. An absolute hero for bringing this country to where it is today. This is just my personal opinion, probably unpopular, but let me be free to state what I feel.
And to add - as of 2013 - laws have changed, death penalty rules are changing. Not changing fast enough, but changing. Hopefully they abolish it entirely asap.